Returns the inherent dimension of the geometry value
g, or NULL if
the argument is NULL. The dimension can
be −1, 0, 1, or 2. The meaning of these values is
given in Section 12.5.2.2, “Geometry Class”.

Returns the minimum bounding rectangle (MBR) for the
geometry value g, or
NULL if the argument is
NULL. The result is returned as a
Polygon value that is defined by the
corner points of the bounding box:

Returns a binary string indicating the name of the geometry
type of which the geometry instance
g is a member, or
NULL if the argument is
NULL. The name corresponds to one of the
instantiable Geometry subclasses.

Returns 1 if the geometry value g
has no anomalous geometric points, such as self-intersection
or self-tangency.
ST_IsSimple() returns 0 if
the argument is not simple, and NULL if
the argument is NULL.